Gas distributor



Nov. 22, 1966 J. E. LOEFFLER, JR, ETAL GAS DISTRIBUTOR 2 Sheets-Sheet Filed Jan. 2, 1964 QUADRANT Fig. 1

1966 J. E. LOEFFLER, JR.. ETAL 3,

GAS DISTRIBUTOR Filed Jan. 2, 1964 2 Sheets-Sheet 2 United States Patent 3,287,090 GAS DISTRIBUTOR John Edward Loeliler, Jr., Lyndhurst, Ohio, and Paul R: Prokish, La Porte, Tern, assignors to piamond Alkali Company, Cleveland, Ohio, a corporation of Delaware Filed Jan. 2, 1964, Ser. No. 335,274 8 Claims. (Cl. 23-277) This invention relates to improvements in apparatus for the production of unsaturated hydrocarbons by the ncomplete oxidation of more saturated hydrocarbons, with oxygen, in a flame reaction, and more particularly relates to improvements in the type of apparatus for the production of such unsaturated hydrocarbons wherein the apparatus includes a mixing chamber for preheated streams of gaseous hydrocarbons and oxygen, a flame chamber into which a plurality of auxiliary streams of oxygen are introduced in order to stabilize the flame which is a source of energy for the reaction, and an intermediate section which may be regarded as a gas-distributor, flamearrester, connecting the flame chamber and the mixing chamber. Still more particularly, the invention relates to improvements in apparatus of the above-described type wherein there is provided in the gas-distributor, flamearrester, section a plurality of regularly spaced groups of symmetrically arranged tubular channels opening into the mixing chamber and the flame chamber.

According to methods well known in the art, unsaturated hydrocarbons may be produced by the incomplete oxidation of more saturated hydrocarbons, with oxygen, in a flame reaction, the most notable of which is the production of acetylene from methane or higher hydrocarbons. Probably the most widely used method involves the incomplete oxidation of methane with oxygen, by separately preheating methane and oxygen, mixing them as quickly and completely as possible in a suitable mixmg chamber, the amount of oxygen used ordinarily being about one-third the stoichiometric amount for complete combustion to carbon dioxide and water, and passing the gas mixture through a gas-distributor, flame-arrester, section leading from the mixing chamber into the flame chamber. The gas-distributor, flame-arrester, section is customarily constituted by a cylindrical ceramic burner block in which there are regularly spaced, symmetrically arranged, tubular channels through which the gas mixture passes from the mixing chamber to the flame chamber at a speed generally in excess of that at which flame propagation of the mixture of the hydrocarbon and oxygen will take place.

However, such an arrangement for the incomplete combustion of a hydrocarbon, and particularly methane, with oxygen, has two rather serious drawbacks, the first of which is the formation of relatively large amounts of carbon which are deposited upon the surface of the gasdistn'butor, flame-arrester, section facing the flame chamher and adjacent surfaces, thus not only diminishing the yield of acetylene, but when formed under the conditions existing in the reaction chamber, such deposits adhere very firmly, and must be removed by mechanical means. In such circumstance, the face of the gas-distributor, flame-arrester, section may often be badly damaged and becomes unfit for further use within a short time. The second of these drawbacks is the matter of providing a stable flame in the flame chamber, i.e., a flame which retains its position in the flame chamber without fluctuation either away from or back toward the gas-distributor, flame-arrester, section.

It has been proposed to overcome both ditficulties by introduction of auxiliary streams of oxygen suflicient to maintain the flame in a relatively fixed position in the flame chamber, such introduction of auxiliary oxygen be- ICC ing made at the periphery of the flame chamber and immediately downstream from the openings of the gas-distributor, flame-arrester, tubes into the flame chamber, and by having that part of the gas-distributor, flame-arrester, section facing the flame chamber in the form of metal conduits surrounding the ends of the tubular channels, in which conduits cooling fluid is circulated, thereby in elfect forming a liquid-cooled single pass heat-exchanger.

It has also been proposed to provide a multiplicity of small-bore oxygen ports (orifices) in the metal wall of a liquid-cooled radiant heat absorber facing the flame chamber, the ports being directed at an angle from the vertical such that the streams of oxygen impinge upon some but not all of streams of the gaseous mixture of oxygen and methane entering the flame hamber. In this proposed arrangement, the oxygen supplied to the ports is by way of conduits arranged between groups of the tubular members passing through the radiant heat absorber of the gas-distributor, flame-arrester, section.

While the flame in the flame chamber may be stabilized in either manner, the introduction of auxiliary oxygen provides small localized flame cones of high-heat radiation which considerably increases the radiant heat flux toward the surface of the gas-distributor, flame-arrester, section facing the flame chamber, which radiant heat must be absorbed and dissipated if the flame side of the gas-distributor, flame-arrester, section is to remain intact for any appreciable length of time during operation of the apparatus, whether fabricated of ceramic material or of metal. Also, and particularly, from the standpoint of commercial production of acetylene from methane and oxygen, merely providing simple fluid-circulating metal conduits surrounding the ends of the tubular channels as a liquid-cooled radiant heat absorber is totally unsatisfactory because of the very high-heat fluxes encountered, which seriously affect the metal surfaces facing the flame chamber, and maintaining the apparatus in satisfactory working condition for any substantial period of time becomes nearly impossible.

During the course of our investigations in the manufacture of unsaturated hydrocarbons, such as acetylene, from gaseous hydrocarbons, such as methane, with oxygen in a flame chamber, and employing a multiplicity of smallbore oxygen ports supplied by conduits arranged between adjacent groups of tubular members in the radiant heat absorber, as described above, as a means for providing an auxiliary supply of oxygen to the flame chamber in order to stabilize the flame therein, it was discovered that flame temperatures and radiant heat fluxes were considerably in excess of those heretofore considered normal in the design of such apparatus. In fact, it was found that heat fluxes of the order of 1,180,000 B.t.u./sq. ft./hr., or about 20 times that accepted as practicable in engineering design work, were to be dealt with.

In such circumstance, if the surface of the gas-distributor, flame-arrester, section facing the flame chamber were fabricated from a high heat-resistant metal alloy, and were water-cooled, the heat radiated to such metallic surface by the main flame and the auxiliary flames in the flame chamber would not be transferred to the water sufliciently rapidly, because of the poor heat conductivity of such metals. The result is that there is a large temperature gradient through the metal wall and thus high internal stresses are generated within the metal, accompanied by comparatively rapid failure, due to cracking at the metal surface adjacent the flame chamber. Accordingly, it is apparent that, if the surface of the gasdistributor, flame-arrester, section facing the flame chamber is of metallic material and a liquid-cooled radiant heat absorber is to be provided surrounding the ends of the gas-distributor tubes entering the flame chamber, either the metal face must be very thin if fabricated from high temperature-resistant alloys, or the face must be made of a relatively more highly heat-conductive metal. However, in order to have a high temperature-resistant alloy conduit the amount of heat encountered, the thickness would be considerably less than practicable for standard commercial fabrication techniques and the mechanical stresses involved.

On the other hand, in such environment, it is appar cut that metals having much greater heat conductivity than those metals resistant to high temperatures would by ordinary standards be considered as out of the question as materials of construction, since it would be expected that such metals would quickly be destroyed by the high heat flux by virtue of the fact that, due to the amount of heat to be transferred by themetal, much of the water circulated in the radiant heat absorber would be vaporized and little or no'liquid would remain in contact with the metallic surface at the face of the gas-distributor, whereby transfer of heat from the metal to the liquid would not take place, but rather the heat transfer would be from metal through vapor to liquid and the good heatconductive metals would be very rapidly destroyed.

As disclosed in application Serial No. 336,896, filed in the names of ourselves and another, it was found that in order to absorb the radiant heat flux involved in apparatus of the type to which the present invention is directed, and still have the temperature gradient through the metal wall of the radiant heat absorbing chamber facing the flame chamber at a sufficiently low level for practical commercial operation, the phenomenon of nucleate boiling of the coolant in the radiant heat absorber adjacent the flame chamber was a necessity. In this regard, the term nucleate boiling refers to the boiling of the coolant initiated at nuclei or tiny centers of active boiling on a metal surface, such nuclei being induced by minute surface cracks or pits or similar imperfections normally present in unpolished metal surface, with the further provision that the minute bubbles of coolant vapor forming at such nuclei are immediately swept away and condensed in the body of coolant, and thus prevented from coalescing and forming a blanket of vapor in the vicinity in which boiling is taking place.

Three factors were found to be requisite in order to insure nucleate boiling of the coolant, the first of which is the velocity of the coolant across the metal surfaces internally of the radiant heat absorber; the second, subcooling of the coolant (the temperature below the boiling point of the coolant at the pressure at which it is introduced into the radiant heat absorber); and third, the geometry of the radiant heat absorber which necessarily bears a relationship to the velocity of the coolant travelling within the absorber. As to the geometry of the absorber, it was found that those parts of the apparatus which would deflect the flow of coolant across the tube sheet facing the flame chamber should be symmetrically arranged so as to provide a plurality of fluidly connected labyrinthine passageways of substantially equal length extending across the absorber from the region of introduction of coolant to the region from which the coolant material may be discharged.

In the'type of apparatus to which the improvement of the present invention is directed, the auxiliary oxygen is supplied by conduits positioned within the radiant-heated absorber above the tube sheet and supported upon regularly-spaced downcomers mounted upon the tube sheet complementing the symmetrical arrangement of tubular channels and coolant deflecting means, such downcomers being in fluid communication with the conduits and the oxygen ports.

A matter of paramount importance and one to which thepresent invention is directed, was found to be in the transfer of heat in the areas of the tube sheet below the downcomers from the oxygen conduits in which the small-bore oxygen ports are located.

In these areas, radiant heat striking the face of tube sheet takes relatively long and oblique paths to the nearest metal surfaces in contact with coolant either by virtue of the placement of the oxygen ports in the tube sheet, or positioning the downcomers on the surface of the tube sheet internally of the absorber, or both. The effects of the internal stresses set up in the tube sheet of the ab-. sorber as a result of this arrangement are readily observable after an extended period of operation as minute surface cracks in the areas involved ultimately leading to serious damageto the tube sheet.

It was found, however, that this condition could be relieved by extending the downcomers to the flame side. of the tube sheet of the heat absorber, and making provision for the auxiliary oxygen ports in a body of material adapted to be inserted into the thus-formed perforations extending over the area of tube sheet immediately surrounding the perforations. It. was also found that such bodies may be constituted of materials of either of two extremes in physical properties, one a highly heatconductive material, or a material having a very high degree of refractoriness sufiicient to withstand the radiant heat fluxes involved, but in themselves very poor heat conductors.

Thus, the bodies may serve both to. shadow or shield the area of the tube sheet adjacent the perforations and to act as auxiliary oxygen distributing members. With the highly heat-conductive materials, for example copper, or copper alloys having this property, radiant heat received at the surface of the bodies is rapidly transferred to the tube sheet and thence to surface in contact with the coolant, whereas with the materials having a high degree of refractoriness, for example, tungsten-carbide, the bodies function for the most part as a shadowing or shielding device, and hence these bodies may be considered as heat-shielding button-like inserts.

It is an object of the present invention to provide improved means for transferring radiant heat in an apparatus for the production of unsaturated hydrocarbons by lncomplete oxidation of hydrocarbons with oxygen in the flame reaction, employing a plurality of auxiliary streams of oxygen into the flame chamber to stabilize the flame in which apparatus there is provided also a liquidcooled radiant heat absorber having a liquid-cooled metal wall facing the flames generated in the flame chamber.

Another object of the invention is to provide means for improved heat transfer in such apparatus having auxiliary supply conduits mounted with the heat absorber and supported upon regularly-spaced downcomers mounted,

on the liquid-cooled metal wall facing the flame chamber and supplying oxygen to oxygen ports in said metal wall, Which means are effective in the areas of the liquid-cooled metal wall facing the flame chamber conforming to the areas of the metal wall adjacent the ends of said downcomers.

These and other objects of the invention willbe apparent to those .skilled in the art from the description which follows hereinafter, and particularly. with respect to the accompanying drawings attached hereto and made a part hereof.

Pursuant to the above objects, the present invention is directed to an improvement in apparatus for the production of unsaturated hydrocarbons by incomplete oxidation of more saturated hydrocarbons with oxygen in a flame reaction, such apparatus having a mixing chamber sorber having a cooling chamber including a metal'tube sheet surrounding the ends of said tubular channels opening into said flame chamber, means positioned within said radiant heat absorber for introducing said plurality of auxiliary streams of oxygen in the said flame chamber through regularly-spaced perforations in said tube sheet between adjacent groups of the openings of said tubular channels into the said flame chamber, which improvement in said means comprises oxygen supply conduits positioned within said absorber and supported upon regularlyspaced downcomers in fluid communication with said conduits and said flame chamber through perforations in said tube sheet, radiant heat-shielding and auxiliary oxygen-distributing member having an essentially hemispherical portion, and a cylindrical portion adaped for insertion in said perforations, said hemispherical portion of said members having conduits therein arranged to direct streams of oxygen toward streams of said gaseous mixture issuing from adjacent groups of said tubular channels opening into said flame chamber, said cylindrical portion having a conduit in fluid communication with said conduits in said hemispherical portion and said perforations in said tube sheet.

In order that those skilled in the art may better understand the principles involved in the present invention, reference may be had to the drawings, in which:

FIG. 1 is a composite of sectional plan views of successive quadrants of the cylindrical gas-distributor, flamearrester, section and the radiant heat absorber of an apparatus to which the present invention is especially effectively applied, the quadrants being observed at progressively lower levels indicated by A, B, C, and D, respectively, with the tubular channels removed, for clarity, in quadrants A.C., inclusive;

FIG. 2 is an elevation of two vertical sections made from the geometrical center of the apparatus in FIG 1 to the lines 22 of FIG. 1 and viewed in the direction indicated by the arrows;

FIG. 3 is a vertical section of an auxiliary oxygen supply conduit through a supporting downcomer and after being preheated, the gaseous mixture then passing into the gas-distributor, flame-arrester, section 6 through distributor tubes 10 to flame chamber 8. Tubes 10, through a portion of their length, may be surrounded by suitable insulating or refractory material in the spaces 12.

The lower portion of the tubes 10 also are surrounded by the liquid-cooled radiant heat absorber member 28 acting as the containing shell of the absorber, comprising lower metal tube sheet 14 and upper metal tube sheet 16, which may also act as a support for the insulating or refractory material in spaces 12. The portion of the tubes 10 passing through the absorber may suitably be placed within simple tubular sleeve members (not detailed) extending from upper tube sheet 16 to lower tube sheet 14, although the rate of gas flow through the tubes 10 is sufficiently high that very little cooling of the gas by the absorber is encountered. A baflfle plate 18 is interposed between the lower and upper tube sheets 14 and 16, respectively, thereby forming fluidly connected adjacent liquid circulation chambers of the radiant heat absorber surrounding the ends of the gas-distributor tubes 10 in the region where they enter the flame chamber and in position to receive heat radiated by the flames in the flame chamber. Mounted upon the lower tube sheet 14 are hollow metal support members 24 for conduits 20, the support members acting as downcomers for carrying the auxiliary supply of oxygen from the conduit 20 through 6 orifice 22 (see detail of FIG. 3) into the flame chamber 8 through orifices 26.

The tubes 10 are preferably arranged in groups and in parallel rows in such a manner that their centers fall on a line parallel to a diameter of the heat absorber and on a line at an angle of 60 to such diameter, the groups constituting three rows of tubes paralleling a diameter of the heat absorber section, particularly shown in quadrant D of FIG. 1, thus providing triangular pitch arrangement to each group of tubes.

The oxygen conduits 20 preferably are placed so as to be interposed between the groups of tubes with the supporting downcomers 24, which also act as coolant deflecting members in the lower cooling chamber, positioned so as to be substantially in register with the symmetrical arrangement of tubular channels 10. In addition, there are preferably provided other metallic coolant deflecting members 30, mounted upon the lower tube sheet 14 and arranged so as to fill out the symmetry of the groups of tubular channels and the downcomers in the outer reaches of the cooling chamber near the inner wall of shell member 28 of the heat absorber. The coolant deflecting members 30 are preferably of the same cross-sectional configuration as the downcomers 24 and tubes 10, shown in FIGS. 1, 2 and 4, as cylindrical. Also, in mounting coolant deflecting members 30 between tube sheet 14 and baflle 18, it is preferred that there be provided a projection which is substantially smaller than the main body of the deflecting member so that such main body is spaced apart from the lower tube sheet to permit the coolant as much access as possible to the heat transfer surface and prevent localized accumulation of vapor, while at the same time retaining the function of the deflecting members.

Oxygen is supplied to conduits 20 through tubes 34 from oxygen header 36, shown inFIG. 1, and the conduits 20 are arranged between adjacent groups of rows of tubular members 10, as noted above, and further so that orifices 26 in the radiant heat shadowing, oxygendistributor, 52, inserted in the lower tube sheet 14, direct the streams of oxygen toward the space between adjacent pairs of gaseous distributor tubes 10 of the rows of tubes immediately adjacent oxygen conduits 20.

As shown in FIG. 3 of the drawings, the body 52, in its preferred form, has a hemispherical portion containing the oxygen conduits 26, fluidly communicating with a conduit 54 in a cylindrical portion of the button-like body 52, the cylindrical portion making it readily adaptable for insertion into downcomers 24 from the flame side of the tube sheet.

Water is'the preferred coolant material, and may be introduced into the cooling chamber formed by the lower tube sheet 14 and baflie 18 through water conduits 38, of which there is preferably more than one, the water being supplied through header 40, and after passing deflecting member 30, upwardly through the perforation 32 centrally located in baflle plate 18, and thence around the tubes 10, through the upper chamber formed by the upper tube sheet 16 and baffle 18 and outwardly through a plurality of ports 42, into chamber 44 formed by innerwall 48 and outerwall 50, and through a second series of ports 46 to a collection chamber not shown. The abovedescribed path of the water circulating in the upper and lower chambers is illustrated by the directional arrows in this portion of the apparatus in FIG. 2, although it will be recognized by those skilled in the art that the water may just as effectively be introduced first into the upper chamber flowing through the central orifice and then through the lower chamber.

As to materials of construction for the button-like radiant heat shielding and auxiliary oxygen-distributor, bodies 52, these are readily fabricated from metals having a high heat conductivity, such as copper, or copper alloys having this property, the high heat conductivity being an advantage in that the radiant heat received from the flame chamber is readily transferred to the absorber both through tube sheet 14 and through the lower portion of the walls of downcomers 24 to surfaces in contact with coolant material. The reason for the hemispherical form of the heat-shielding, auxiliary oxygen-distributor, buttonlike bodies 52 is that radiation from the flames is received at a minimum of the surface whereby such radiated heat to be transferred through the spherical portion to the tube sheet is likewise minimized and the portion of the lower tube sheet 14 immediately adjacent and in contact with bodies 52 is preserved for a much longer period of time than is the case where the auxiliary oxygen is supplied through orifices in the tube sheet of the absorber as described above.

This arrangement of the button-like bodies 52 also has the added advantage that, in the event the portion extending beyond the tube sheet 14 is for any reason damaged so that the oxygen conduits 26 no longer function properly, a button is readily removed from a downcomer 24, either by prying or drilling the metal from the portion or the downcomer 24 in which the cylindrical part of the button is inserted, and a new one is equally readily replaced.

Conversely, the button-like bodies may be fabricated from materials having a very high degree of refractoriness, such as tungsten-carbide, silicon-carbide, porcelain, or high-purity alumina, which have the ability to withstand the high temperatures encountered in the flame chamber and, at the same time, shadow a portion of the lower tube sheet 14 with which they are in contact, from the radiant heat generated by the auxiliary oxygen flames. Such materials, while presenting a basically sound approach to the problems solved by the present invention in heat shielding the tube sheet and distributing the auxiliary oxygen streams, are not .as easily fabricated, and secured in the downcomers 24, as are those made of highly heatconductive material such. as copper or copper alloys, since the cylindrical portion of a copper or copper alloy button, as above-described, is readily inserted into a portion of downcomer 24 and secured in place by the use of the technique of furnace brazing.

It is to be understood that although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited, sincechanges and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

What is claimed is:

1. In an apparatus for the production of unsaturated hydrocarbons by incomplete oxidation of more saturated hydrocarbons with oxygen in .a flame reaction, such apparatus having a mixing chamber for said hydrocarbons and oxygen, a flame chamber into which a plurality of auxiliary streams of oxygen are introduced to stabilize the position of said flame, and having a gas-distributor, flamearrester, section interconnecting said chambers, and having a plurality of symmetrically-arranged groups of parallel rows of tubular channels opening into said mixing chamber and said flame chamber, a liquid-cooled radiant heat absorber interposed between said mixing chamber and said flame chamber, said absorber having a metal tube sheet forming one boundary of said flame chamber and surrounding the portion of said tubular channels opening into said flame chamber, and means positioned within said absorber for introducing said plurality of auxiliary streams of oxygen into said flame chamber through regularly spaced perforations in said tube sheet between adjacent groups of the openings of said tubular channels into said flame chamber, the improvement in said means comprising tubes in fluid communication with said means for introducing said auxiliary streams of oxygen and inserted in said perforations, radiant heat shielding and auxiliary oxygemdistributing button-like bodies having an essentially hemispherical portion and a cylindrical portion adapted for insertion in said tubes, said hemispherical portion having conduits therein arranged to direct streams of oxygen toward streams of said gaseous mixture issuing from adjacent groups of said tubular channels opening into said flame chamber, said cylindrical portion having a conduit in fluid communication with said conduits in said hemispherical portion and saidtubes in said tube sheet.

2. The apparatus of claim 1 wherein said tube sheet is circular, said tubular channels are arranged in groups of three parallel rows such that the centers of said chan-.

nels opening into said flame chamber fall on a line parallel to a diameter of said tube sheet and on a line at an angle of 60 to such diameter, and said heat-shielding and oxygen-distributing bodies are positioned between adjacent groups of the openings of said tubular channels into said flame chamber.

3. The apparatus of claim 2 wherein the tubes inserted in said perforations in said tube sheetrfor introducing auxiliary streams of oxygen into said flame chamber complement the symmetry of said tubular members in said radiant heat absorber.

4. The apparatus of claim 3 wherein the conduits in said hemispherical portion of said radiant heat-shielding and auxiliary oxygen-distributing bodies direct streams of oxygen between adjacent streams of said gaseous mixture issuing from adjacent tubular channels opening into said flame chamber.

5. The apparatus of claim 4 wherein said heat-shielding auxiliary oxygen-distributing bodies are constituted of high heat conductive metal.

6. The apparatus of claim 4 wherein'said heat-shielding auxiliary oxygen-distributing bodies, are constituted of high temperature-resistant refractory material.

7. The apparatus of claim 5 wherein the metal contains copper. I

8. The apparatus of claim 6 wherein the high temperature-resis'tant refractory material is silicon carbide.

No references cited.

MORRIS O. WOLK, Primary Examiner.

J. H. TAYMAN, J R., Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3,287,090 November 22, 1966 John Edward Loeffler, Jr., et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, line 5, for "conduit" read conduct llne 24, for "336,896" read 333,896

Signed and sealed this 22nd day of August 1967.,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN AN APPARATUS FOR THE PRODUCTION OF UNSATURATED HYDROCARBONS BY INCOMPLETE OXIDATION OF MORE UNSATURATED HYDROCARBONS WITH OXYGEN IN A FLAME REACTION, SUCH APPARATUS HAVING A MIXING CHAMBER FOR SAID HYDROCARBONS AND OXYGEN, A FLAME CHAMBER INTO WHICH A PLURALITY OF AUXILIARY STREAMS OF OXYGEN ARE INTRODUCED TO STABILIZE THE POSITION OF SAID FLAME, AND HAVING A GAS-DISTRIBUTOR, FLAMEARRESTER, SECTION INTERCONNECTING SAID CHAMBERS, AND HAVING A PLURALITY OF SYMMETRICALLY-ARRANGED GROUPS OF PARALLEL ROWS OF TUBULAR CHANNELS OPENING INTO SAID MIXING CHAMBER AND SAID FLAME CHAMBER, A LIQUID-COOLED RADIANT HEAT ABSORBER INTERPOSED BETWEEN SAID MIXING CHAMBER AND SAID FLAME CHAMBER, SAID ABSORBER HAVING A METAL TUBE SHEET FORMING ONE BOUNDARY OF SAID FLAME CHAMBER AND SURROUNDING THE PORTION OF SAID TUBULAR CHANNELS OPENING INTO SAID FLAME CHAMBER AND MEANS POSITIONED WITHIN SAID ABSORBER FOR INTRODUCING SAID PLURALITY OF AUXILIARY STREAMS OF OXYGEN INTO SAID FLAME CHAMBER THROUGH REGULARLY SPACED PERFORATIONS IN SAID TUBE SHEET BETWEEN ADJACENT GROUPS OF THE OPENINGS OF SAID TUBULAR CHANNELS INTO SAID FLAME CHAMBER, THE IMPROVEMENT IN SAID MEANS COMPRISING TUBES IN FLUID COMMUNICATION WITH SAID MEANS FOR INTRODUCING SAID AUXILIARY STREAMS OF OXYGEN AND INSERTED IN SAID PERFORATIONS, RADIANT HEAT SHIELDING AND AUXILIARY OXYGEN-DISTRIBUTING BUTTOM-LIKE BODIES HAVING AN ESSENTIALLY HEMISPHERICAL PORTION AND A CYLINDRICAL PORTION ADAPTED FOR INSERTION IN SAID TUBES, SAID HEMISPHERICAL PORTION HAVING CONDUITS THEREIN ARRANGED TO DIRECT STREAMS OF OXYGEN TOWARD STREAMS OF SAID GASEOUS MIXTURE ISSUING FROM ADJACENT GROUPS OF SAID TUBULAR CHANNELS OPENING INTO SAID FLAME CHAMBER, SAID CYLINDRICAL PORTION HAVING A CONDUIT IN FLUID COMMUNICATION WITH SAID CONDUITS IN SAID HEMISPHERICAL PORTION AND SAID TUBES IN SAID TUBE SHEET. 